In a typical mobile communications system, mobile units are supported by radio networks coupled to different mobile switching centers (MSCs) providing an interface between the radio networks and the public switched telephone network (PSTN). In traditional circuit-switched environments, an MSC controls both the signaling and bearer paths for a call. When a mobile unit participating in a communications session roams from the service area of one radio network to the service area of another radio network, the communications session may be handed-off between the MSCs coupled to the radio networks. When a hand-off occurs between two MSCs, the source MSC establishes a circuit-switched connection to the next switch in the network providing service to the mobile unit. The source MSC has to maintain the original circuit-switched connection, providing an anchor for the bearer path and the second circuit-switched connection. Additional connections may need to be added if the mobile unit roams into other network service areas, and these connections may need to be linked to the original connection.
IP networks have begun to replace MSCs. Accordingly, systems and methods are needed for handing-off mobile communications sessions between IP networks coupling radio networks to the PSTN